Natural cork has been used as a closure for bottles containing wine and other liquids for many years. Due to its resilience, elastic properties, water impermeability and, in earlier times, low cost, cork is widely used throughout the wine industry worldwide for sealing bottles.
Availability of cork has in recent time decreased due to more widespread demand and limited supply. However, cork quality has also become a concern to wine producers as a result of undesirable reactions between the cork and the wine. Problems from cork taint are estimated to be as high as 6% of all bottled wine. One form of cork taint occurs when trichloroanisole (TCA) present in the cork migrates into the wine giving rise to "off" flavours. The costs involved have become an unacceptable burden on wine producers. Accordingly, there is a need for an inexpensive alternative to natural cork, which has no such reaction with wine.
A number of synthetic closures are presently available on the market. One type of closure comprises a substantially cylindrical polymeric body having radial resilient flanges along the length of its shank adapted to seal about the inside neck of a container, and a crown which overlies the bottle opening. Such closures are commonly used for sparkling wines. A disadvantage of such closures is that they require special corking machinery for their insertion into bottles and they cannot be utilised in an unmodified bottling operation.
Other types of polymeric closures available are generally identical in size and shape to conventional corks and can be utilised in standard bottling operations without needing to modify machinery. One group of known polymeric closures are manufactured from foamed ethylene vinylacetate (EVA) copolymer. The polymer is generally foamed with a foaming agent such as azodicarbonamide (ABFA) or ozodecarbonoxide. Other polymers have also been proposed for use for such closures. Closures made from Linear Low Density Polyethylene (LLDPE) blended with ionomers have also been disclosed.
The polymeric stoppers known in the art suffer from a number of disadvantages primarily as a result of the polymeric material from which they are made. First, the EVA polymers which have the desired flexural properties may exhibit some odour or flavour taint which may affect the contents of the bottle and EVAs which do not exhibit taint are not likely to have the desired flexural properties. The foaming agents suftable for use with EVAs similarly may demonstrate some flavour or odour taint of the contents of the bottle which they are sealing. EVAs are also prone to degradation during manufacture of a closure.
Polyvinylchlorides (PVCs) and ionomers are unsuitable as they impart undesirable taint to the wine.
LDPEs including LLDPEs although they do not impart significant undesirable tastes to the wine, do not have adequate flexural properties in particular, inadequate elastic recovery in order to form an adequate seal.
Accordingly there is a need for a polymeric closure for a container which satisfies many or most of the following performance criteria:
a) Does not impart any taint to the contents of the container, especially where such contents are wine; PA1 b) Does not scalp any flavours from the contents of the container to any significant extent; PA1 c) Has suitable flexural properties such that it can be adequately deformed and inserted into the opening of the container, yet will recover sufficiently to maintain a long-term fluid impermeable seal between the closure and the container PA1 d) Can be removed in one piece from said container when desired using conventional apparatus, such as a corkscrew, without structural failure PA1 e) Can be coloured to resemble natural cork and optionally printed upon PA1 f) Can be used in conventional corking machinery PA1 g) Can be mass produced cost effectively. PA1 i) a density of between 0.910 g/cm.sup.3 and 0.885g/cm.sup.3 ; PA1 ii) a molecular weight distribution of 2 or less; and PA1 iii) a melt index of between 2 and 30, more preferably between 2 and 10. PA1 i) a density of between 0.910 g/cm.sup.3 and 0.885 g/cm.sup.3 ; PA1 ii) a molecular weight distribution of about 2 or less; and PA1 iii) a melt index of between 2 and 30. PA1 i) a density of between 0.900 g/cm.sup.3 and 0.888 g/cm.sup.3 ; PA1 ii) a molecular weight distribution of 2 or less; and PA1 iii) a melt index between 2.2 and 3.5, or a blend of 2 or more polyethylenes having these properties. PA1 M.sub.N =number average molecular weight
"Scalp" refers to the undesirable tendency of some substances to extract flavours from a liquid. it is an object of the present invention to provide a polymeric closure which meets one or more of the above performance criteria.